Rolling bearings are commonly used in the field of aviation. Typically, aviation turbomachines such as gas turbine engines use rolling bearings for supporting rotary shafts inside a structural piece. The rolling bearings are essentially constituted by balls or rollers retained in races formed by outer and inner bearing rings. In an aviation turbomachine, ball bearings are generally used for holding axial loads and roller bearings for holding radial loads in the turbomachine.
It is known to use oil to lubricate and to cool rolling bearings in a turbomachine. Given the heating of the turbomachine and the high speed of rotation of its shafts, simple lubrication by injecting oil only during maintenance of the turbomachine is not sufficient. It is therefore necessary to have recourse to “dynamic” lubrication of the rolling bearings. Dynamic lubrication consists in causing the oil to circulate continuously around a feed circuit. Oil is thus injected between the rings of the bearings and subsequently leaves the bearings, thereby extracting the heat produced in such bearings. The oil is then filtered and de-aired so as to separate out air from the oil. An oil enclosure and an air enclosure supporting the rolling bearings enable a closed environment to be provided so as to ensure that lubricating oil does not escape into the engine proper.
Dynamically lubricating rolling bearings as described above presents the major drawback of requiring an oil circulation circuit to be provided that includes recovery scoops, feed pipes, and a pump, thereby increasing the weight of the turbomachine. Providing oil and air enclosures also contributes to increasing the weight of the machine.
In order to reduce the size of such enclosures, patent EP 0 769 631 proposes a ball or roller bearing that makes use of the dynamic energy created by rotation of the shaft supported by the balls or the rollers in order to drain the lubricating oil. A drainage circuit is provided via orifices for draining the lubricating oil that are formed through one of the rings of the bearing. That type of drained rolling bearing enables a major portion of the lubricating oil to be recovered.
It is also known to provide rolling bearings with oil films of the “squeeze film” type in order to reduce the vibration generated by the high speed of rotation of the turbomachine shafts supported by the rolling bearings. Typically, oil under pressure is confined between the outer bearing ring and a structural piece of the bearing. At the contact surface between the ring and the structural piece, the oil under pressure thus acts as a damper. In general, oil-damped bearings of this kind are sealed by means of annular gaskets interposed between the outer bearing ring and the structural piece. The oil film is thus defined between two sealing gaskets.
Nevertheless, that type of oil-damped bearing presents a problem of leaktightness. It is found in practice that the oil confined between the two sealing gaskets tends to flow outside the oil film. The presence of the sealing gaskets does not enable such leaks to be avoided. In particular, oil flows appear not only beside the oil enclosure, which is acceptable, but also beside the air enclosure. Such flows beside the air enclosure are particularly harmful to proper operation of the turbomachine.